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Gases, Liquids, and Solid fuels

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Fuels are those chemicals that, when combined with oxygen and an ignition source, burn and liberate heat. Fuels come in three general categories; Gasses, Liquids, and Solids. It should be noted that absolutely no fuel will burn unless it's in a gaseous form. Look closely at a wood fire or candle flame, notice that the actual flame is slightly away from the wick or surface of the wood. As a candle is lit, the heat of the match causes a little of the wax in the wick to be heated to its vapor-point. Once the wax has become a vapor (gas) it mixes with air, which contains about 20% oxygen, and combustion starts. As the wax vapor burns it heats more wax to its vapor point and so on. Wood, coal, gasoline, alcohol or any oil, burn in exactly the same way. We will now examine a few of the more popular types of fuels in each category.

Gaseous Fuels:

Methane; Can be produced by refining oil, but is most commonly produced by the decomposition of biological wastes. Usually, homemade methane can not be compressed into a liquid due to its high oxygen content, it will detonate under pressure. Methane is stored as a gas in very low-pressure bag like structures. Homemade methane has a low energy content per cubic foot,due in part to high CO2 & nitrogen content. Methane has been used to run internal combustion engines that generate electricity at sewage treatment plants in the US and elsewhere. The, somewhat, more successful use of methane has been in third world countries to convert animal waste to cooking, heating and small engine fuel. Requires a lot of animal waste, constant attention to the bacterial cooking process, and preparations for small, spontaneous, fires and soft explosions. A difficult, messy and odiferous process to manage.

Butane; A product of refining oil. When compressed into a liquid form has a boiling point a little below the freezing point of water or about +30F. Stored as a liquid in very low-pressure tanks and generally used in disposable lighters and some camping stoves.

Propaine; Sometimes called LPG "Liquefied Petroleum Gas" A product of refining oil. When compressed into a liquid form it has a boiling point of about -45F. Stored in low-pressure tanks, (less than 300 PSI), at the point of usage, it is used in large quantities for heating, cooking, emergency generators, and to a lessor extent as an automobile fuel.

Natural Gas; Pumped from wells drilled into underground natural gas pockets. If compressed into a liquid form, which it never is, it would have a boiling point of about -260F. Delivered via underground pipelines to factories and homes, it is used in very large quantities for heating, cooking, emergency generators, and to a much lessor extent stored in high-pressure tanks, (two to three thousand PSI, but still a gas), and used as an automobile fuel.

Hydrogen Gas; Made from water by the application of electricity. When compressed into a liquid form it has a boiling point of about -420F. Generally stored at atmospheric pressure in large thermos bottles or in a hydride-matrix, it is used in industry and to power rocket ships. Hydrogen has been used experimentally to power automobiles and in fuel cells to make electricity. In its current state of development it is not a viable form of energy for the average person.

Butane, Propane, and Natural Gas have a near infinite storage life. A hundred-year-old tank of propane, assuming it doesn't develop a leak, will be just as good as a new tank of propane. Most pressure vessels must be examined or tested by a professional periodically to insure their safety. Most prudent refueling stations will not refill a portable propane tank after it's over a specific age, regardless of its appearance, (Times vary from state to state) Nor will they refill any rusty or dented tanks.

Some gases are stored as a liquid in pressure vessels, others like Natural gas or Hydrogen are generally stored as a gas in large bag like structures or, in the case of liquid hydrogen, in well insulated large scale thermos bottles. All gases can be converted to a liquid by either cooling or compression. For instance, on a cold winter day you can carry liquid butane around in an open bucket, or you can make gaseous butane into a liquid, even at or above room temperature, by forcing it into a sealed container with about 5 pounds of pressure. As long as you keep the butane container securely sealed it will remain a liquid at any reasonable temperatures. On cold days, below 30F, butane will not come out of its container, so it would be a poor choice for heating your home in the winter. Remember to keep your disposable lighters in you pocket in the winter, to keep them warm enough to light. To carry propane around in an open bucket would require a winter day of about -45F. And to make it a liquid at or above room temp requires over 100 pounds of pressure. Notice that the lower the boiling point the higher the pressure at room temperature, if its to remain a liquid.

Liquefied gasses are thousands of times smaller in volume than their gaseous versions making the liquid form a much more efficient way to store gaseous fuels. This is all fine and good until we get to gasses that have very low boiling points like natural gas or hydrogen. These gases have such a low boiling point, -300F or lower, that if kept in a pressure vessel at room temperature they would generate pressures in the tens of thousands of pounds per square inch. We just can't make pressure tanks strong enough to contain liquid hydrogen, oxygen, nitrogen, or natural gas at room temperatures, even if we could, the tanks would need walls a foot thick and would weigh several tons. Oxygen and hydrogen are stored as a liquid in the large center fuel tank on the space shuttle, but instead of a sealed pressure tank, the shuttle tank is actually a large, well-insulted, thermos bottle. The liquid gases are poured in and allowed to vent as they slowly boil off, no high pressures are needed.

Liquid Fuels:

Alcohol; Two types: 1) Methyl Alcohol , refined from oil, or wood products & poisonous if ingested. 2) Ethyl Alcohol, produced by fermentation and considered an adult beverage by some. It is a liquid at temperatures up to about +180F and contains more energy per gallon than butane or propane. Often mixed with gasoline to reduce pollutants or, in the case of ethyl alcohol, used to absorb water from gasoline. (Note: methyl alcohol will not absorb water) Ethyl alcohol is hydroscopic and will absorb water from the air, eventually reducing its fuel quality to uselessness. Must be kept in an airtight container. An alcohol fire is invisible and can cause great harm before it is noticed. Use great care when handling alcohol fuels.

Gasoline; Refined from oil, also can be synthesized from coal. It is a liquid at temperatures up to about +190F and contains more energy per gallon than alcohol. Most commonly used as a motor fuel. Should be stored outside and/or far from any open flames or sparks and in an airtight container. Invisible fumes can be released from vented containers, which are toxic and can come in contact with an ignition source. Gasoline and alcohol can generate static electricity as they are poured from a container, especially plastic containers, spouts or funnels, and cause a spark, which could start a fire. Never pour gasoline while inside any structure. Always fill your lawnmower or generator outside and away from anything combustible. Never refuel a running motor, fuel can spill on the sparkplug or hot engine parts and start one hell of a fire. Always have a fire extinguisher at the ready while working with any liquid fuels. BTW, Never use gasoline or alcohol to help start a trash-fire or barbecue, fumes will permeate the material to be burned and when a match is brought close a soft explosion can occur, scattering burning material in all directions. Not to mention, taking off your eyebrows or worse.

Kerosene; Refined from oil. It is a liquid at temperatures up to about +225F and contains more energy per gallon than gasoline. Most commonly used as a heating or lamp fuel. Not nearly as volatile as gasoline or alcohol and can be used to assist in the starting of a trash-fire. Low volatility also makes kerosene a relatively safe fuel. Little work is required to allow a diesel engine to run kerosene.

Diesel & stove oil; Refined from oil. Diesel & stove oil are almost identical and can be used interchangeably in most vehicles and furnaces or stoves. It is a liquid at temperatures over +275F and contains a little more energy per gallon than kerosene. Most commonly used as a motor fuel and heating oil. A little less volatile than kerosene and can also be used to assist in the starting of a trash-fire. Low volatility also makes diesel & stove oil a relatively safe fuel. Diesel engines, by their design, require absolutely water free and very clean fuels. Diesel engines can burn almost anything that can be burned in a simple oil lamp. Olive oil, peanut oil and other plant-derived oils, if very pure and free from water, can be used in most diesel engines.

Liquid fuels such as alcohol, gasoline, kerosene, and diesel or stove oil when stored in a container larger than just a few gallons will breathe or try to. As the day warms through the morning the contents of a fuel tank will warm and expand. If a fuel storage tank is sealed the pressures may become so great as to rupture the tank or weaken the seals. During the night the inverse will occur, this reduction in pressure can, and does routinely, collapse fuel tanks. I have seen several hundred-gallon tanks, bigger than a car, squashed like a beer can.

Large tanks must be vented. This poses another problem. As a fuel tank cools, in the evening, it sucks moisture-laden air into the tank. As the air cools inside the tank water condenses out onto the inside walls of the tank. As the water droplets run down the inside of the tank they eventually find their way to the bottom of the tank. Remember that water is heavier than all liquid fuels. As the days and months go by, more and more water is drawn into the fuel tank. Eventually this will cause the tank to rust out, causing massive leaks, and/or the water will make a home for a specific species of anaerobic bacteria that thrive in the fuel/water interface and will ruin your fuel. Underground tanks suffer less from breathing, due to the ground's insulation properties, but will still breathe on an annual bases due to the seasonal changes in ground temperature. Above ground tanks can easily by relived of their water by periodically draining them from a bottom-mounted valve. Subterranean tanks can be pumped clean of water by the use of a long pipe shoved down through the filler cap to the bottom of the tank, and a pump used to extract the water from the bottom of the tank. There are several chemical treatments listed under the "Long Term Storage" link to your left, that will reduce the effects of water or bacterial damage to your fuel.

Solid Fuels:

Dung; Dried cattle dung has been used as a source of fuel for thousands of years. Fairly low in energy per pound, and somewhat odiferous when burned, animal dung is not my first choice in fuels.

Wood; The oldest fuel used by humans. Wood has a wide spectrum of energy per pound, depending the plant species from which it comes. The wood with the highest energy density is white oak, (nearly as high as anthracite coal). Generally the heavier the dried wood is, the higher its energy content and more efficient is its usage. A few woods, such as ironwood, just won't burn, and a few others can be dangerous if burned. Poison oak, ivy, or sumac should not be burned, its smoke can be very irritating or even lethal to some people.

Coal; Mined from the earth, coal was produced millions of years ago by the compression of plant and animal materiel. There are three kinds of coal; Lignite, a soft, brown coal that releases a lot of pollutants as its burned, Bituminous coal that burns somewhat cleaner than lignite, and Anthracite a very hard and shiny black coal that contains more energy per pound and burns the cleanest. Sometimes coal is exposed at the surface of the earth and can be harvested by simply picking it up off the ground. Some Native Americans have used coal in their campfires for thousands of years.

Indoor fires in fireplaces or stoves can coat the inside of the chimney or smoke pipe with combustible residue that, eventually, will ignite and can burn your house down. It is recommended that you periodically clean and inspect your chimney to reduce the chances of a fire.

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